@@ -6,16 +6,35 @@
 """
 Heap's algorithm
 https://en.wikipedia.org/wiki/Heap%27s_algorithm
+https://www.geeksforgeeks.org/heaps-algorithm-for-generating-permutations/
 """
 from typing import List
 
 
+def heap_permutation(elements: List[int], size: int, res: List[List[int]]):
+    """Generating permutation using Heap Algorithm """
+    # if size becomes 1 then prints the obtained
+    # permutation
+    if size == 1:
+        res.append(elements[:])
+        return
+    for i in range(size):
+        heap_permutation(elements, size - 1, res)
+        # if size is odd, swap first and last
+        # element
+        # else If size is even, swap ith and last element
+        if size & 1:
+            elements[0], elements[size - 1] = elements[size - 1], elements[0]
+        else:
+            elements[i], elements[size - 1] = elements[size - 1], elements[i]
+
+
 def all_perms(elements: List[int], n: int):
     if n == 1:
         yield elements[:]
     else:
-        for i in range(n-1):
-            for hp in all_perms(elements, n-1):
+        for i in range(n - 1):
+            for hp in all_perms(elements, n - 1):
                 yield hp
             if n % 2 == 0:
                 elements[i], elements[n-1] = elements[n-1], elements[i]